Method for controlling an electromagnetic valve drive mechanism for a gas exchange valve in an internal combustion piston engine

ABSTRACT

A method for controlling an electromagnetic actuator for a cylinder valve in a piston-type internal combustion engine with the actuator being operatively connected to the cylinder valve and moveable back and forth between two electromagnetics, counter to the force of at least one restoring spring. The current supplied to the electromagnetics is controlled with the aid of a sensor arrangement and via an engine control unit such that the current supply to the catching electromagnet, i.e., the electromagnet being approached by the moveable armature of the actuator, is controlled so as to move the armature slowly toward the respective pole face. Moreover, in order to regulate the valve play during the closing movement of a cylinder valve, the current supply to the catching electromagnet is controlled such that the valve initially touches down softly on its seat and that following the valve play, the armature touches down softly on the pole face.

BACKGROUND OF THE INVENTION

A major problem with electromagnetic valve drives for operating acylinder valve in a piston-type internal combustion engine is that inthe presence of a valve play, the valve touchdown speed must becontrolled so as to reach extremely low values (below 0.2 m/s). This isdue to the fact that relative to the armature distance, the valvetouchdown point changes for thermal reasons (variation of the valveplay) during the operation. The armature furthermore must still safelyreach the pole face after the valve has touched down. If the currentsupply is too low, the armature reverses direction too early and knocksthe valve off again. If the current supplied is too high, the resultingarmature touchdown speeds- are too high, which leads to an acousticproblem as well as rebounding actions and, in the worst case, also to arenewed, uncontrolled valve opening and thus a failure of the completesystem.

The invention is explained in further detail with the aid of schematicdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an electromagnetic valve drivewith control.

FIG. 2 shows the speed curves for armature and valve during a closingmovement.

FIG. 3 shows the speed curves for armature and valve when reaching theclosed position on a larger scale.

FIG. 4 illustrates the curves for the valve path and the armature pathas well as the current curve in dependence on the time when using astate-of-the-art control.

FIG. 5 shows the speed curves for valve and armature during the closingmovement for a control based on the method according to our invention.

FIG. 6 shows the curves for the armature path and the current independence on the time when using the method according to the invention.

FIG. 7 is a schematic illustration of the basic layout of the control inthe form of a block diagram.

FIG. 8 is a schematic illustration of the sequence of steps for theactuation method according to the invention, shown with the aid of ablock diagram.

FIG. 9 is the the block diagram according to FIG. 8, supplemented with a“monitor.”

FIG. 10 is the block diagram according to FIG. 9 with a link between theengine control and the monitor.

FIG. 11 is the block diagram according to FIG. 10, supplemented by apre-estimation unit.

FIGS. 12A and 12B are block circuit diagrams showing circuitmodifications when using a “monitor.”

FIGS. 13 to 15 illustrate the design and function of a magneto-resistivemovement sensor.

FIGS. 16 and 17 show embodiments of microwave resonator path sensors.

FIG. 18 shows an optical variant of a resonator path sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The basic principle of an electro magnetic valve drive of this type,including its control, is shown schematically in FIG. 1.

An electromagnetic valve drive for actuating a cylinder valve 2essentially comprises an actuator 1 with a closing magnet 3 and anopening magnet 4, which are arranged at a distance to each other. Anarmature 5 can be moved back and forth between these magnets, counter tothe force of a readjusting spring, namely an opening spring 7 and aclosing spring 8.

The “traditional” arrangement for the opening spring and the closingspring is shown in FIG. 1 in the closed position. With this arrangement,the closing spring 8 is directly effective by means of a spring plate2.2 that is connected to the shaft 2.1 of the cylinder valve 2. Theguide rod 11 of the electromagnetic actuator is separated from the shaft2.1. As a rule, a gap in the form of the so-called valve play VS existsin the closed position. The opening spring 7 in turn supports itself ona spring plate 11.1 on the guide rod 11, so that in the center positionwhere no current is supplied to the magnets, the guide rod 11 supportsitself on the shaft 2.1 of cylinder valve 2 while the opening spring 7and the closing spring 8 are effective in opposite directions. It isalso possible to provide a single return spring in place of the openingspring 7, which is designed to build up a corresponding restoring forceeach time the armature 5 passes over the center position. A separateclosing spring 8 is therefore not needed. With an arrangement of thistype, however, the guide rod 11 must be connected to the shaft 2.1 ofthe cylinder valve by means of a corresponding coupling element, whichtransmits the back and forth movement of the armature in the same way tothe cylinder valve 2, but which nevertheless permits a valve play.

The electromagnets 3 and 4 of actuator 1 are actuated via an electronicengine control 9, in accordance with the predetermined control programsand in dependence on the operating data such as speed, temperature,etc., which are supplied to the engine control.

The actuator 1 is assigned a sensor 10, which makes it possible todetect the actuator functions. The sensor 10 is shown schematicallyherein. Depending on the sensor design, it is possible to detect thepath traveled by the armature 5, for example, so that the respectivearmature position can be transmitted to the engine control 9. Ifnecessary, the armature speed can be determined with the aid ofrespective computations in the engine control 9, so that the currentsupply to the two electromagnets 3, 4 can be controlled in dependence onthe armature position and/or in dependence on the armature speed.

It is not necessary for the sensor 10 to be arranged on the side of theextended guide rod 11, as shown. Rather, it is also possible forcorresponding sensors to be arranged in the pole face region of therespective electromagnet, or on the side of the armature 5.

The engine control 9 furthermore comprises means for detecting thecurrent and the voltage for the respective electromagnet 3 and 4, aswell as for changing the current curve and the voltage curve. Theactuator 1 of cylinder valve 2 can be actuated fully variable via theengine control 9, for example with respect to start and end of theopening times, in dependence on preset operating programs, if necessarysupported by corresponding performance characteristics. An actuationwith respect to the height of the opening stroke or even the number ofopening strokes during a closing time is possible as well.

A current control requiring data on the actual movement or position ofthe armature as input signal is necessary to achieve low touchdownspeeds for the armature 5. As long as no valve play exists, a controlbased on the armature position is sufficient. However, if a valve playexists, the situation is rather problematic on the closing side. Thearmature speed and thus also the valve speed must already have a verylow value of approximately 0.2 m/s or lower when the valve touches downon the valve seat (must be at least in the low-speed range).

In FIG. 2, the situation is demonstrated for a “normal” valve touchdown,meaning without the use of the method according to the invention. Thearmature speed over the path traveled by the armature is shown as adrawn-out line. The position for the opened case is shown on the extremeright. An armature stroke of 8 mm was selected here as example. Thearmature position when the armature rests against the pole face of theclosing magnet is shown on the extreme left at 0, 0. Thus, a closingmovement starts at the extreme right position of the picture, at 8 mmand a speed of 0. The speed then increases until approximately thecenter position between the pole faces is reached (at approximately 4mm). If the armature is operated “normally” (not controlled), the valvestill arrives at the valve seat with a relatively high speed ofapproximately 1.1 m/s, particularly if there is a noticeable valve playof, for example, 0.4 mm (cold 0 engine). In this position, the armaturemovement is separated from the valve movement. The valve is stoppedabruptly (interrupted line) and the speed drops to below zero, meaningthe valve rebounds.

The armature initially slows down, but its speed increases once moreshortly before touchdown and the armature touches down with a speed ofapproximately 0.5 m/s. In the meantime, the armature speed has droppedto nearly zero. With a further reduction in the catching current level,the armature would reverse directions before reaching the pole face andthe system would fail.

The region where the valve and the armature touch down is shown enlargedin FIG. 3. The separate armature and valve movements are clearlyrecognizable. Initially, the armature and valve move together withoutvalve play (curve segment v_(a+v)). As soon as the valve touches down onits seat, valve and armature separate and perform separate movementsowing to the valve play. (The dashed line is for the valve; thedrawn-out line is for the armature.)

The curves for the armature position (drawn-out line), the valveposition (dashed line) and the current (dash-dot line) are plotted abovethe time in FIG. 4. Initially, the current level shows that a constantcurrent value is maintained. However, the current initially collapses ifthe armature is getting very close since the counter-induced voltageexceeds the supply voltage. Following this, the preset value for thecurrent level is raised to ensure a secure catching of the armature. Thenew level can be reached because the armature is almost at a standstilland because the lack of armature movement initially does not induce anadditional counter-voltage.

FIGS. 5 and 6 show the conditions when using the method according to theinvention for the exemplary embodiment illustrated in FIGS. 2 and 4. Thespeed curve over the path traveled by the armature, in turn, is shown inFIG. 5. The curve for the armature speed differs significantly from theuncontrolled curve. Initially, the armature is accelerated morefollowing the separation from the valve than in theunregulated/uncontrolled case. With a closer approach, however, thecurrent is drastically reduced again to the level required for stoppingthe armature (approximately 1.5 A for this example).

With a corresponding design of armature and yoke, it may even make senseto supply current flowing in the opposite direction (reversal of currentdirection) to produce rejecting forces.

The armature path curve and the current curve are plotted over the timein FIG. 6. A valve touchdown speed of approximately 0.2 m/s can beachieved as a result of controlling the current curve.

The block diagram in FIG. 7 shows the actuation by the actuator. Theengine control 9 in this case predetermines the point in time at whichthe movement (valve closing) is initiated. This occurs through shuttingdown the current with the closing coil in the current driver 12 (theexample shows that no current is supplied to the closing coil).Depending on the respective armature position, which is determined via aposition detection device 13, for example a sensor 10 plus processingcircuit, the current is then controlled in such a way that the armaturemaintains, if possible, a path/speed profile that can be predetermined.The position controller 14 is used for this.

FIG. 8 shows that two control or regulation operations are planned.During the movement of the cylinder valve, the control is initiallyassumed by the unit designated the valve position controller 14. Thedesign for this unit can be identical to that for unit 14 in FIG. 7.However, it must be taken into consideration that the target, which mustbe reached with low speed, is not the pole face, but rather the valveseat, that is to say the pole face position plus the valve play.

As soon as the seating of the valve in the seat is detected (or that thevalve is immediately adjacent to it), a switch to the armature controloccurs. This is illustrated in FIG. 8 in that a “valve separationdetector” 17 determines that the valve has touched down on the seat andthe current presetting device for the current driver 12 then switches tothe output of the armature position controller 15. (In reality, thearmature position controller can physically be the same unit, which issimply controlled in another mode.) The valve separation detector canobtain its information from the sensor 10 or the position detector orthe output signal of the position detection 13. Based on the currentand/or voltage curve on the magnet, it can draw a conclusion for theseparation of valve and armature or determine this via a separate sensor16. A sensor of this type can simply be a contact that closes when thetwo electrically conductive parts separate (e.g. armature bolt and valveshaft). In order to avoid problems with dirt on the contacts, however,it is also possible to detect a capacity change between the separatingcomponents. A non-conductive separating layer is required for thisbetween the two components.

The armature current controller can also perform its function via a timecontrol since only the distance of the valve play must still be bridged.For example, the current curve in this case is plotted above the timeand in dependence on the existing valve play. Thus, it also becomespossible to use a valve position sensor in place of the armatureposition sensor since the information on the armature position is nolonger that important.

FIG. 9 shows an expanded control that is particularly useful if theposition is to be detected with cheap sensors. The problem in that caseis that the path signal must be differentiated in order to obtain aspeed information. However, with a noisy or interrupted signal this canbe achieved only insufficiently. The problem can be remedied with amonitor 19 containing a model of the actuator (e.g. in the form ofdifferential equations for the connection between acceleration, speedand armature position, as well as information on the armature and valvemass, the spring forces, etc.). Finally, the speed curve that ispossible in principle can be anticipated within limits by the system.The model can then be initialized at the start of the movement. Theexact position and the speed are known at that point in time. The newinformation on the measured position 13 as well as the variable valuesfor the condition determined by the model, if necessary, flow into themonitor (into the model) as new input variables and can then be used tocorrect the actual output variables for path and speed. Furthermore, aself-calibration (adaptation) of the model in the monitor can takeplace. For example, if the monitor determines that the friction ishigher than provided so far for the model, new parameters for thecorresponding variable can be set automatically.

Also, specific parameters for improving the parameter-setting of themodel by the engine control, for example depending on the load (gasforces at the outlet valve), or the engine temperature (estimation ofvalve play, friction, etc.) can be fed into the model (see also FIG. 10,the connection between 11 and 19).

In addition to setting up a purely mechanical model, it is also possibleto take into account the magnetic forces as well. This requiresknowledge of the actually existing current supply, as shown in FIG. 6(connection from 12 to 19 in FIG. 10).

The quality of the controller itself can also be improved if it can beestimated ahead of time how the introduced measures (change of currentlevel) will influence the armature. For this, a predictor 20, a“pre-estimation unit,” is made available to the controller 14 inaccordance with FIG. 11. The predictor 20 furthermore contains a systemmodel and is therefore able to assess the effects of these measures. Ifthe measures are considered not sufficient or too strong, the controllercan also be corrected (“called back”).

The predictor 20 can furthermore also have an “intelligent” design, sothat it can adapt automatically to changing model parameters.

Particular attention must be paid to providing a cost-effective designas well as to ensure the highest possible precision when detecting thearmature or valve position. In particular during the last approach phasewhere the speed is already relatively low and the path information mustbe very exact, the resolution limit for a possibly requiredanalog/digital conversion (quantization) can present a problem. Thisresolution can be improved in that prior to the conversion, therespectively actually estimated value for the position (e.g. from themonitor 19) is initially deducted from the value detected by the sensor,meaning before the value is digitized. FIG. 12 shows the return 21 ofthe position signal from the monitor 19 to the position detection 13.

FIG. 12A shows an example of an embodiment for the position detection.The return signal 21, which is made available in digital form by themonitor, is supplied to a D/A converter 22. The output of the D/Aconverter 22 thus supplies in an analog form the value determined by themonitor for the position. With the aid of a subtracter 24, this value issubtracted from the signal provided by a position sensor, which isinitially raised to the correct level by a processing circuit 23.Following the subtracter, only the difference to the position presentlydetermined by the monitor is available. The signal range for this signalis naturally considerably smaller than that for the original positionsignal. Thus, its level can be raised with the aid of an amplifier 25prior to the A/D conversion 26. The A/D converter subsequently suppliesthe signal for the difference detected by the monitor between the pathinformation and the current, new path information in a digital form tothe monitor 19. This monitor, if necessary, can obtain the new positioninformation by adding the previously detected signal 21 and the newdifference information.

Other exemplary embodiments are possible as well. For example, the A/Dconverter and/or the D/A converter can be integrated into the monitor(FIG. 12B).

According to the invention, the position and/or the speed of thearmature is measured continuously with a sensor in order to control asoft touchdown and these values are used for a closed-loop control ofthe actuator. The invention proceeds on the assumption that an effectiveclosed-loop control of the armature speed or the valve speed is possibleonly during the last portion of the movement, meaning shortly beforereaching the respective end position, because of the dynamiccharacteristics of the system. Nevertheless, it is necessary tointervene at an earlier point in time to be able to reach the requiredcurrent level. The invention provides that parameters are determinedduring the first portion of the movement, which parameters arecorrelated with the cylinder inside pressure. The method of the smallesterror square rate is used for this by looking at the trajectory v(s) inthe status space (v=speed; s=position). Depending on the parametervalues, the voltage is set to a constant level once a specific pathposition s₁ is reached. Once an equilibrium of forces (dv/dt=0) isreached, a nonlinear controller is preferably activated, which switchesthe voltage on or off, depending on the deviation (v-v(s)) of themeasured speed for a desired curve v(s). In accordance with theinvention, energy is fed with low loss and via a bridge circuit backinto the vehicle onboard system once the voltage is switched off,meaning the respective coil is operated with the supply voltage. Aparticularly effective closed-loop control according to the invention ispossible as a result of the speed at which the current drops once it isswitched off.

For one preferred arrangement, the requirement dv/dt=0 is detecteddirectly through a derivation and filtering of the path signal.

The requirement dv/dt=0 for another preferred arrangement is replaced bythe requirement I>=I_(max), meaning the voltage is shut down and thecontroller activated once a predetermined current level I_(max) isreached.

The switch-on position S_(on) and the current threshold I_(max) for onepreferred arrangement are expressed in dependence on the supply voltagethat is measured and the parameters, which reflect the pressure insidethe cylinder. This can occur either through a functional connection or aperformance characteristic.

The desired curve v(s) for one preferred arrangement is selected to beflat during the last portion of the movement, so that the control canensure a low touchdown speed, even with sensor errors.

For one preferred arrangement, the desired curve v(s) is for speedslower than 0.3 m/s since the response time of the control in that caseis short enough to realize a closed-loop control, relative to the systemidle time.

The flat desired curve of one preferred arrangement is expanded enough,so that the area of valve play can be bridged and so that valve andarmature can touch down at a low speed.

The valve play of one preferred arrangement is measured during the firstpart of the opening phase of the valve in that the abrupt drop in thearmature speed is measured during the impact with the valve. Theexpansion of the slow movement segment can thus be adapted to the actualvalve play.

The spring-mass-system of one preferred arrangement can be designed suchthat the distance from the earliest possible point of reaching anequilibrium of forces to the end position on the opening and closingside is long enough to bridge the valve play and compensate for sensorerrors. For this, an armature with low eddy currents is preferably used,for example made of a sintered material, to increase the range bylowering the maximum required current level for the equilibrium offorces.

To increase the low-speed range for the path just prior to the endposition, the holding magnet is briefly supplied with current. Thus, alow maximum speed is reached and the earliest point on the path curve,for which a force equilibrium can be achieved, is further removed fromthe end position. For one preferred arrangement, the energy tappedmechanically in the process is fed back electrically by using anarmature with low eddy currents and a corresponding clocking stage,preferably in a bridge circuit.

The sensor used for one preferred embodiment is a digital path sensor.

The raw sensor signals of one preferred embodiment are processed withthe aid of a status monitor, such that the quality of the path/speedsignal and the current signal is improved by using information on thesystem behavior of the actuator. The status monitor of a particularlypreferred arrangement uses the parameters measured during the initialphase of the movement, meaning during the armature release, which arecorrelated to the counter pressure. For one particularly preferredarrangement, a mean value is formed for the sensor signal during thephase when the armature makes contact in one of the end positions, withthe goal of compensating a possibly existing offset error and/oramplification error of the sensor and thus reduce the requirements forthe sensor with respect to the temperature stability.

The controller for a particularly preferred arrangement is a two-pointor a three-point controller with feedback branch, which contains adigital filter. This filter is preferably a low-pass filter with asuitably matched characteristic. The scanning time for the completearrangement is preferably at 20 μs.

The end phase of one particularly preferred arrangement is a switchingend stage, for which the rise times and the decay times fall below 5 μs.

In one preferred arrangement, the communication between the touchdowncontrol of the actuator and the actuating engine control is designed insuch a way that the engine control delivers information on the expectedcylinder inside pressure, which are used in addition to the measuredparameters and which are correlated to the actual cylinder insidepressure. The touchdown control furthermore supplies information back tothe engine control, for example the measured valve play, parameters thatare correlated to the actual cylinder inside pressure, parameterscorrelated to the actuator wear and parameters correlated to theactuator temperature.

In another preferred embodiment, the invention is used if the valve playis compensated hydraulically. Advantageous in that case is a strongdamping of the vibrations in the speed/path curve, which normally occurwhen the armature bolt impacts with the valve and a valve play ispresent. The valve play makes it more difficult to determine parametersthat are correlated with the counter pressure.

The information quality must meet high requirements during the actuatorcontrol, particularly for the realization of the method according to theinvention. The requirements for resolution, reproducibility and accuracyare above the requirements met by standard analog sensors, which arepresently used in this application field. The reason for this, amongother things, is that the concentration of electrical stray fieldsdirectly adjacent to the engine is immense and that the interferencelevel absorbed by the lines is very high.

A digital signal transfer therefore represents a possible solution toreaching the desired quality.

Another advantage can be achieved if the measured signal is obtaineddirectly with the aid of a digital measuring operation. The advantagesin this case are: no A/D conversion, cheap and robust electroniccomponents, etc.

Some of the principles presented here are based on digital measuringmethods. For this, a digital pulse is issued for each path or a binarybit pattern for each path segment. With the relative positiondetermination, the absolute position must be derived with the aid of analgorithm and by taking into account the rest position and the maximumpath traveled by the armature. The speed can be determined via the timedifference between the pulses or the bit pattern changes.

Preferred measuring methods are those, which can be realized asintegrated components, including the signal processing.

Digital methods for a relative position measurement are:

optical methods with slotted disk;

optical methods based on the interferometer principle, as described inthe following;

magnetic methods, using a magneto-resistive matrix without binarycoding, as described in the following;

resonator measuring principles (frequency depending on the geometricposition of the armature path), as described in the following.

Absolute measuring principles, which sensibly result in a binary codecorresponding to the position:

optical methods with, for example, a charge-coupled device CCD line,

magnetic method with a magneto-resistive matrix, configuredone-dimensional or two-dimensional, in contrast to singularmagneto-resistive sensors, which are known.

FIGS. 13 to 17 show and describe a path measurement using amagneto-resistive measuring principle on the basis of measuring cellmatrixes. The magneto-resistive matrix 30 (XMR matrix) can be arrangedas shown in FIGS. 13 and 14. A position magnet 31 is attached to theguide rod I 1. The evaluation circuit for the XMR matrix 30 provides theinformation which sensor of the matrix for the sensor line receives amaximum signal. That is the position with which the position magnet 31is correlated on the guide rod 11, meaning the actual path position.

FIG. 14 shows another embodiment. The signal processing is limited togenerating pulses during the change of the maximum from one singlesensor to the next one. One preferred embodiment concerns the generatingof a pulse code that is displaced by 90° for the direction detection. Anembodiment with special magnet geometry, for example the embodimentshown in FIG. 15, is suitable for increasing the resolution. Through thearrangement of two position magnets 30.1 and 30.2, a narrow region withhorizontally extending field lines is created in the center, whichpermits a larger path between matrix and position magnet.

Another option for increasing the resolution is the use of the Noniusprinciple. For this, several position magnets are mounted on the guiderod 11.

A compensation of mechanical tolerances relative to the rotationalgeometry of the guide rod is possible through an evaluation and bytaking into account the level distribution.

The accuracy for compensating mechanical tolerances can conceivably beincreased further through a special arrangement of two matrixes, forexample arranged opposite each other.

FIGS. 16 to 18 show and describe measurements of the path and speedusing a microwave resonator principle.

FIG. 16 shows an arrangement that can be fitted onto the top of anactuator. The valve shaft in that case is frictionally connected to theelectromagnetic valve (EMV) armature and the guide rod 11, so that theguide rod 11 reflects the path position of the armature plate.

The free end of guide rod 11 projects into a resonator housing 35, whichis filled in part with a dielectric 36, preferably in the areas that arenot reached by the guide rod during the linear movement. An oscillator37 is connected via a coupling device (capacitive or inductive) to theresonator. This arrangement makes it possible to use the path traveledby the armature as the frequency-determining component of an oscillator37. The path signal information 41 as well as the speed information 42can be made available to the engine control via a reference oscillator38 in a mixer or a frequency demodulator 39 with subsequent filteringand signal processing 40.

FIG. 17 shows a comparable arrangement, which also can be fitted on topof an actuator. The guide rod 11 indicates the path position of thearmature plate. The guide rod 11 forms a displaceable part of a coaxialresonator 35 with a fixed part that is filled with a dielectric. Theguide rod 11 can travel the linear path and can thus change thereflection characteristics of such a coaxial resonator arrangement asfunction of the EMV armature movement.

By way of the insulation 43, the oscillator 37 is connected to the fixedresonator part between the center conductor 44 and the housing. A pathsignal 41 as well as the speed information 42 can be made available viaa reference oscillator 38 in a mixer or a frequency demodulator 39, withsubsequent filtering and signal processing.

A path or speed measurement obtained by using an optical resonatormeasuring principle is shown and described with the aid of FIG. 21.

FIG. 18 shows an arrangement in which an optical variant of a resonatormeasuring principle is illustrated, which can also be attached to theguide rod 11 of an actuator.

The guide rod 11 indicates the path position of the armature plate. Inorder to provide the armature position, a magnetic arrangement 45 thatis connected to the shaft causes the effect of the magnetic field on thezone 46. The component 46 thus represents an optical conductor, forwhich the optical characteristics, preferably the refractive index,represent a function of the magnetic field intensity. The completearrangement is screened against interfering fields and external fields.

The optical conductor 46 is sealed off on one side by an optical mirror47 and is connected via coupling elements 48, for example a glass fiberand/or a polarization turning element and/or an optical impedanceadaptation to semiconductor fibers, actuated via current signal 50 anddriver 51. A semiconductor (HL) laser 49 transmits a beam in thedirection of sensor 52. By way of the element 48, 46, 47, 46, 48, 49,the second beam of the HL laser 49 also impinges on this sensor, so asto interfere. The detector signal 53 thus measures the interferencebased on changes in the path length of the two beam paths. A path lengthis then changed implicitly by means of the magnetic field and the magnet45 through varying the refractive index in the element 46, thus forminga measure for the path of the guide rod 11. A change in the length ofelement 46 when using optical materials, for which the refractive indexis not a function of the magnetic field intensity, results from gluingtogether a magneto-restrictive material 46.1 and the optical element 46.Thus, the magnetic field effects a mechanical change in the length ofelement 46.

A path and speed signal is determined by evaluating the detector signal.

What is claimed is:
 1. A method for actuating an electro-magneticactuator for activating a cylinder valve provided with a valve stem in apiston-type internal combustion engine, with possible valve play betweenthe valve stem and a guide rod for the actuator that acts upon the valvestem and is connected to an armature that is guided back and forthbetween pole faces of two electromagnets, arranged at a distance fromeach other, counter to the force of at least one restoring spring,wherein the current supply to the electromagnets is respectivelycontrolled with the aid of a sensor arrangement and via an enginecontrol unit, said method comprising: controlling the current such thatthe current supply to the electromagnet being approached by the armatureso as to move the armature with a low movement speed toward therespective pole face, and, in order to regulate a valve play during theclosing movement of the cylinder valve, further controlling the currentsupply to the electromagnet being approached such that initially thevalve touches down softly on its seat and, following the valve play, thearmature touches down softly on the respective pole face.
 2. A methodaccording to claim 1, wherein the current control is adjusted such thatthe armature maintains a predetermined path/speed profile in dependenceon a detected position of at least one of the armature and the valve. 3.A method according to claim 1, wherein the current supply for theelectomagnet being approached is switched to said further control andthe armature is moved separately toward the pole face if a valve playexists when the valve touches down on the seat.
 4. A method according toclaim 3, further including recording the touchdown of the valve on theseat via a valve separation detector.
 5. A method according to claim 1,wherein the control of the current supply to the electromagnet beingapproached for guiding the armature after the valve touches down on itsseat, occurs during a specified interval, in dependence on thepredetermined valve play.
 6. A method according to claim 1, wherein thesubsequent detection with sensors of at least one of the valve positionand the armature position occurs via an electronic model of theactuator, which contains actuator parameters essential to the function.7. A method according to claim 6, further including adding actualoperating data from the engine control to improve the setting ofparameters in the electronic model.
 8. A method according to claim 1,further including checking the respectively initiated control measuresvia a pre-estimation unit containing an electronic model of the actuatorto estimate their future effects, and correcting the controller controlunit if necessary.
 9. A method according to claim 1, further includingdetermining the parameters correlated to the cylinder inside pressure atthe start of the cylinder valve movement.
 10. A method according toclaim 1, further including: when switching off the voltage present atthe electromagnet being approached, feeding energy back into the vehicleonboard system via a bridge circuit.
 11. A method according to claim 1,further including during the valve opening in the first part of theopening phase, detecting the valve play via detection of a drop in speedwhen the armature impacts with the valve.
 12. A method according toclaim 1, including designing the spring mass system, consisting of theactuator, the readjustment spring and the cylinder valve, such that thedistance between the earliest possible point for reaching theequalization of forces to the end position on the opening side and onthe closing side is long enough to bridge the valve play and to balancesensor errors.
 13. A method according to claim 1, including supplyingthe information concerning the cylinder valve movement, detected via thetouchdown control, to the engine control unit.
 14. A method according toclaim 1, further including generating digital signals for detecting atleast one of the path and the speed of the armature and making thesedigital signals available to the engine control unit.
 15. A methodaccording to claim 1, further including: in order to extend the distancetraveled by the armature at low movement speed before reaching its endposition, controlling the armature separation from the holdingelectromagnet by briefly supplying current to the holding electromagnetso that a lower maximum speed in the direction of the electromagnetbeing approached by the armature is achieved, and thus the earliestpoint at which a balance of forces can be reached is farther removedfrom the end position.